Continuously Diagnosing the Instrumentation Electrical Loop - Emerson Automation Experts

Continuously Diagnosing the Instrumentation Electrical Loop

My friends in Chanhassen have been hard at work on the usability front. I connected with Emerson’s Alexander Miller to find out what’s the latest with the Rosemount 3051 pressure transmitter.

Alex pointed to two new innovative features — Local Operator Interface (LOI) and Power Advisory Diagnostic. I thought we might dig into the Power Advisory Diagnostic more closely in this post, come back, and look at the Local Operator Interface in a future post.

The thought behind the development of this diagnostic was to be able to detect and identify problems associated with the electrical loop occurring between the Rosemount 3051 and 3051S Series transmitters and the control system. Additionally, alerting the operations and maintenance teams before such issues negatively impact measurement values and control of the process. This diagnostic detects problems associated with corrosion, failing power supplies, wiring issues, and water intrusion. The diagnostic can be set up using any HART communication system (i.e. Field Communicator or AMS Device Manager), in three steps (see video below).

Alex noted that the Power Advisory Diagnostic tells you there is an issue occurring within your electrical loop, be it in a device or anywhere in the electrical loop between the transmitters, power supply, or control system I/O. Early detection can prevent costly outages by alerting you of a potential issue before you lose your measurement, helping avoid costly outages and dangerous trips to the field.

Alex and his team put together a demonstration video at the 2011 Emerson Exchange to highlight the Power Advisory Diagnostic in action.

3051 and 3051SThey also have developed a new website together with the Rosemount 3051S Series of Instrumentation. New product videos, Interactive Demo Tours and Brochures of the Rosemount 3051 and 3051S Series instrumentation demonstrate these new capabilities and how they can be used to positively impact your operations and maintenance efforts.

I know from my days as a systems engineer working with our operations teams on offshore platforms, tracking down wiring issues can be a very frustrating and time-consuming task. Intermittent problems would keep us troubleshooting for days and cause spurious trips and unplanned downtime.

Power Advisory Diagnostic would have been a great tool to have to help us locate problems early and help minimize the downtime and troubleshooting time.


  1. This is what I call, the “Automation of Automation”.

  2. Jonas Berge says:

    I agree. The leakage current and increased resistance result in a wrong measurement as the result of loose or corroded screw terminals or ground faults, so for a 4-20 mA circuit a transmitter might be trying to send a certain value but as a result of excessive impedance you might get less at the receiver resulting in a wrong PV indication giving operators the wrong picture. Control and alarms will also not work appropriately. Therefore, if 4-20 mA is used, this kind of signal circuit diagnostics is a good idea. In my personal opinion, more 4-20 mA devices should have this capability.
    These 4-20 mA loop failures are undetected (covert) which is generally dangerous. Such analog signal problems are hard to detect because they are ‘on-scale’ meaning they are wrong, but still within the range of 4 mA and 20 mA so they appear to be correct to the system even though they are invalid. That is, a problem with a 4-20 mA signal may go undetected. Increased impedance may be due to loose or corroded screw terminals, or it could be ground fault. Water ingress creating a partial short is another common cause:
    Use of a digital bus or wireless protocol can prevent the problem. Digital communication statistics such as provided in DeltaV detects installation issues affecting the communication. Failures in communication systems are generally overt which is generally safe. If the data received by a final element or any receiving device is not timely, and is not valid, it is very easy to detect. The ability to diagnose the digital communication to detect errors is an important advantage of digital protocols (fieldbus or wireless) over hardwired systems (4-20 mA or on-off).

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